[Misc][MacOS] fix bfloat16 error

[reidliu41]

• In MacOS When try to request the API, and serve the model with auto dtype, it would cause the BFloat16 error , it should fixed before 11696 based on description currently it should still need to to modify cpu_extension.cmake to activate(and hard to make it).
• seems update it in 5c4c08f#diff-7eaad0b7dee0626bf29d10081b0f0c5e3ea15a4af97e7b182a4e0d35f8346953

vllm serve qwen/Qwen1.5-0.5B-Chat

line 276, in rms_norm
ERROR 05-16 11:28:20 [engine.py:161]     torch.ops._C.rms_norm(out, input_contiguous, weight, epsilon)
ERROR 05-16 11:28:20 [engine.py:161]   File "/opt/miniconda3/envs/vllm/lib/python3.12/site-packages/torch/_ops.py", line 1158, in __call__
ERROR 05-16 11:28:20 [engine.py:161]     return self._op(*args, **(kwargs or {}))
ERROR 05-16 11:28:20 [engine.py:161]            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ERROR 05-16 11:28:20 [engine.py:161] RuntimeError: "rms_norm_impl" not implemented for 'BFloat16'

So it would be better to bring it back.

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[Isotr0py]

I think it's just because of a mistake in CPUPlatform here:

vllm/vllm/platforms/cpu.py

Lines 33 to 39 in 67da572

	elif sys.platform.startswith(
	"darwin") and self.get_cpu_architecture() == CpuArchEnum.ARM:
	# TODO: change this condition to check if the platform support bf16
	# instead of checking the OS. For instance M2 shall supports bf16
	# already. But we need to modify `cpu_extension.cmake` to activate
	# the feature in the build.
	return [torch.bfloat16, torch.float32]

Correct bfloat16 to float16 there should work as well.

[reidliu41]

Thank you for your confirm. Just tested, it worked